1. Field of the Invention
This invention relates to an image pickup apparatus having a deep focal depth and an image pickup apparatus system which are preferable for endoscopic observations for example.
2. Description of Related Art
Conventional image pickup apparatuses include an image pickup apparatus the focal depth of which is expanded by selecting an image with good contrast from two images that are different in focus position to combine the selected images.
As one example of such conventional image pickup apparatuses, as in disclosed in Japanese Patent Kokai No. Hei. 09-116807 and Japanese Patent Kokai No. 2003-078802 respectively for example, there are image pickup apparatuses in which one bundle of light rays is divided into two bundles of light rays by a half prism and two image sensors capturing images formed by the two divided bundles of light rays respectively are placed with the lengths of the optical paths of the two bundles of rays to the image sensors made to differ from each other so that the focus positions at which the two images are formed on the image sensors respectively are different from each other.
FIG. 11 is a view schematically showing a structure of the image pickup apparatus disclosed in Japanese Patent Kokai No. Hei. 09-116807.
The image pickup apparatus disclosed in Japanese Patent Kokai No. Hei. 09-116807 is configured to have a structure in which: light traveling from an object 20 to be imaged is made to pass through an imaging lens 51 and then is divided into two bundles of light rays by a two division prism 52 to have two optical paths, the two division prism 52 being provided with a half mirror; one of the two divided bundles of light rays is imaged by an image sensor 53 that is placed at an image-forming position; and the other is received by an image sensor 54 that is placed to be slightly shifted from the image-forming position. Besides, in FIG. 11, the numeral reference 55 denotes a high pass filter, and the numeral reference 56 denotes an adder which adds to imaging output signals captured by the image sensor 53 high-frequency signals passing through the high pass filter 55 of imaging output signals captured by the image sensor 54.
FIG. 12 is a view schematically showing a structure of the image pickup apparatus disclosed in Japanese Patent Kokai No. 2003-078802.
The image pickup apparatus disclosed in Japanese Patent Kokai No. 2003-078802 is formed to have a structure in which: light traveling from an object 20 to be imaged is made to pass through an imaging lens 61 and then is divided into two bundles of light rays by a prism 62 to have two optical paths, the prism 62 having a half mirror structure; and the two divided bundles of light rays are imaged by image sensors 63 and 64 which are different from each other in depth of field and which are placed so that the rear depth of field of one of the image sensors 63 and 64 is equal to the front depth of field of the other. Besides, in FIG. 12, the numeral references 65 and 66 denote movement devices that move the image sensors 63 and 64 in the directions of the optical axes running respectively, respectively, the numeral reference 67 denotes an operation-processing device that calculates a distance from the imaging lens 61 to each of the image sensors 63 and 64, the numeral references 68 and 69 denote drive circuits that operate the movement devices 65 and 66 respectively, respectively, and the numeral reference 70 denotes an image-synthesizing device.
Also, as another example of such conventional image pickup apparatuses, for example, there is an image pickup apparatus in which a beam splitter is placed on one CCD and two images are formed on areas of the CCD different from each other, like an electronic endoscope which is disclosed in Japanese Patent Kokai No. 2004-313523.
FIG. 13 is a view schematically showing an inner structure of the front portion of an electronic endoscope provided with the image pickup apparatus disclosed in Japanese Patent Kokai No. 2004-313523.
In the image pickup apparatus disclosed in Japanese Patent Kokai No. 2004-313523, light traveling from an object 20 to be imaged (living tissue) is made to pass through an objective lens 71 and then is divided into two light bundles by a first prism 72 to have two optical paths, the first prism 72 including a beam splitter 72a, and light transmitted by the beam splitter 72a is reflected by a second prism 73 including a total reflection mirror 73a that totally reflects light transmitted by the beam splitter 72a. And then, light reflected by the beam splitter 72a is imaged by a light-receiving part 74a of a CCD 74 and the light reflected by the total reflection mirror 73a is imaged by a light-receiving section 74b of the CCD 74. Besides, in FIG. 13, the numeral reference 75 denotes an opening for illumination, and the numeral reference 76 denotes a light guide for guiding illumination light for illuminating the object 20.
In addition, as yet another example of such conventional image pickup apparatuses, like a fluorescence observation apparatus shown in FIGS. 5 and 6 of Japanese Patent Kokai No. 2010-220890 for example, there is an image pickup apparatus in which: an afocal bundle of light rays is formed at an intermediate part of an optical path; an optical-path dividing element is placed on the part of the optical path at which the afocal bundle of rays is formed, to divide the optical path; and positions of image-forming lenses on the divided optical paths are adjusted respectively or optical members are inserted on the optical paths respectively so that the lengths of the optical paths up to positions at which images are formed respectively are made to differ from each other, in order to form two images on one image sensor.
FIG. 14 is a view schematically showing a structure of the image pickup apparatus shown in FIG. 5 of Japanese Patent Kokai No. 2010-220890.
In the image pickup apparatus disclosed in Japanese Patent Kokai No. 2010-220890, light traveling from an object to be imaged is made to pass through an objective lens 81, light with a wavelength longer than exciting wavelength is reflected by a dichroic mirror 82 and white light the wavelength of which is shorter than the exciting wavelength is transmitted so that the light traveling from the object is divided into two bundles of light rays. In addition, the white light which is transmitted by the dichroic mirror 82 and the wavelength of which is shorter than the exciting wavelength is divided into two bundles of light rays by a half mirror 83. And, the light transmitted by the half mirror 83 is focused on the focal plane of an image sensor 88 by a condenser lens 85, and the light reflected by the half mirror 83 is reflected by a mirror 90 and is focused on a position that differs from the focal plane of the image sensor 88 by a condenser lens 86. Besides, in FIG. 14, the numeral reference 89 denotes an exciting light cut filter which cuts the exciting light of light reflected by the dichroic mirror 82, and the numeral reference 84 denotes a condenser lens by which light transmitted by the exciting light cut filter is focused on the focal plane of an image sensor 87.